Thermoplastically processible polyamides can be divided into semicrystalline and amorphous homo- and copolyamides. The semicrystalline polyamides form an important group of commercial thermoplastics. Shaped articles produced from them are distinguished by high strength, rigidity, toughness and surface hardness, by good abrasion behaviour, and excellent resistance to chemicals and good stress crack resistance. However, the usefulness of these semicrystalline homo- and copolyamides (for example the high melting point homopolyamides PA 6 and PA 6, 6) is substantially reduced by their tendency to absorb water and the associated reduction of the glass transition temperature which causes a loss of rigidity and strength.
Rigid amorphous copolyamides are generally produced from aromatic dicarboxylic acids and diamines having a crystallization-inhibiting structure and can contain further comonomers such as amino acids, lactams, and salts of diamines and dicarboxylic acids. The properties of such copolyamides can be varied within wide limits by the choice of the monomers used in each case.
As already mentioned, the glass transition temperature drops due to moisture absorption, which in turn causes a reduction in the upper temperature at which it can be used. If rigid amorphous copolyamides are used, for example, in boiling water, a drop in a glass transition temperature (Tg) of up to about 100.degree. C. is possible and this considerably restricts the usefulness of articles produced from these polymers because some of them completely lose their shape. Amorphous copoloyamides are described, for example, in the following patents: GB 619,707, CH 449,257, U.S. Pat. No. 2,494,563, U.S. Pat. No. 3,842,045, U.S. Pat. No. 3,840,501, JP 72/11,502, U.S. Pat. No. 2,969,482, U.S. Pat. No. 3,597,400, DE 21 59 803, and CH 624,970.
It is also known to use polymeric-in particular dimerized-fatty acids for the production of polyamides and copolyamides. These materials are used, for example, in adhesive and lubricant polymer chemistry. The structure and the properties of dimerized fatty acids are described in detail, for example in the Henkel-Emery/Goud a(NL) brochure entitled "Empol Dimer and Polybasic Acids Technical Bulletin 114). These dimerized fatty acids are obtained from monomeric unsaturated fatty acids (usually containing 18 carbon atoms) by a specific polymerization reaction. There are many products having different ratios of monofunctional, difunctional, trifunctional, and polyfunctional acids. Types having a high dimer content (for example 90% and, in particular, 97%) are preferred for the production of thermoplastic polyamides.
Dimerized fatty acids can also be used in polyamides for surface coatings and adhesives (cf. U.S. Pat. No. 3,231,545). Alcohol-soluble additives for printing inks are described in BE 804,604 and GB 1,129,195. Copolyamides of diamines of the so-called dicycane type, i.e. 4,4'-diaminodicyclohexylmethane or derivatives thereof with dimerized fatty acid and a linear dicarboxylic acid containing 6 to 10 carbon atoms are described in U.S. Pat. No. 3,717,598. These products have a low glass transition temperature and a low modulus of elasticity are are therefore unsuitable for many technical applications.
In DE-A 1,720,832, there are described polyamides based on cycloaliphatic diamines (e.g. 3,3'-dimethyl-4,4'-diamino-dicyclohexylmethane), dimerized fatty acid which can be partially replaced by other aliphatic dicarboxylic acids, including cycloaliphatic or aromatic dicarboxylic acids, as well as additional monomers such as aminocarboxylic acids and lactams. The molar content of the dimerized fatty acid, based on the carboxylic groups, must be at least 25%. Examples in which aliphatic dicarboxylic acids are used are the only ones which are described specifically. These products are tough plastic materials having high tensile strength and elongation, and which are used as molding powder, adhesives, and in the form of the films or sheets.
Thermoplastically processible plastic materials which have high rigidity and strength and which maintain these properties under the influence of moisture, in particular in contact with boiling water, are required for many commercial applications. Preferably, the moisture absorption should be so low that the glass transition temperature is only slightly reduced.